Method for the production of ozone using a plasma jet



March 14, 1967 A. v. GROSSE ETAL METHOD FOR THE PRODUCTION OF OZONEUSING A PLASMA JET Filed Aug. 21, 1963 5 Sheets-Sheet l 5 5 R Y mww M ma W WW A Mi K #3 March 14, 1967 A. v. GROSSE ETAL 3,309,300

METHOD FOR THE PRODUCTION OF OZONE USING A PLASMA JET Filed Aug. 21,1963 5 Sheets-Sheet 2 BQ/ u/ /Wm rAi ATTORNEYS March M, 1%? A. v. GROSSEETAL 3,3093% METHOD FOR THE PRODUCTION OF OZONE USING A PLASMA JET FiledAug. 21, 1963 3 Sheets-Sheet 5 so no I30 I50 K CAL/MOLEHQ uouto OXYGEN30o COLLECTION\ GRAMS/HR [00 WW M, a t

I eAsEous OXYGEN CIOLLEOTION LITERS/NHN O (BASED ON GAS) INVENTORS Afirm M Q$$ am? 3 M's BY W, M Y

ATTORNEYS United States Patent f 3,309,300 METHOD FOR THE PRODUCTION OFOZONE USING A PLASMA JET Aristid V. Grosse, Haverford, and Charles S.Stokes, Willow Grove, Pa, assignors to The Welsbach Corporation, Phiadelphia, Pa., a corporation of Delaware Filed Aug. 21, 1963, Ser. No.303,550 12 Claims. (Cl. 204176) This invention relates generally to theproduction of ozone and more particularly to a method and apparatus forthe production of ozone using a plasma jet.

If an explosive gas or an explosive mixture of gases is subjected toconditions which will initiate a flame, an explosion can develop in thebody of the gas if the flame can be maintained. 'If the flame can bequenched in a short distance, no combustion occurs and therefore noexplosion can take place. The distance in which the flame must bequenched to prevent explosion is known as the quenching distance orquenching diameter. This varies with the particular gas or gas mixtureand temperature and pressure conditions.

It has been known that ozone can be held in a vessel in highconcentrations or in substantially pure form where material has beenadded to an explosive gas or explosive mixture of gases which aresubjected to conditions which will initiate a flame if the flame isquenched in a short distance. We have found that ozone may besynthesized by a new method involving the use of an inert gas plasma jetquenched by liquid oxygen.

Accordingly, it is an object. of this invention to provide an improvedmethod and apparatus for synthesizing ozone.

Another object of this invention is to provide an improved method andapparatus for synthesizing ozone using a plasma jet.

A further object of this invention is to provide an improved method andapparatus for synthesizing ozone which is simple in operation andeconomical in construction.

In carrying out this invention in one form thereof, an inert carrier gasis subject to an electrical discharge in a plasma generator, the inertgas being used as a plasma carrier. The high thermal energy produced bythe inert gas are both evaporates and dissociates liquid oxygen which isfed into the arc. The dissociated atoms then either recombine withthemselves or react with oxygen molecules to produce ozone. The arc isquenched by excess liquid oxygen which is not dissociated. The solutionof ozone and liquid oxygen is passed to a collection chamber from whichthe ozone may be recovered by a conventional recovery process.

In another feature of this invention, an inert carrier gas is subject toan electrical discharge in a plasma generator. Oxygen is then subject tothe influence of the plasma jet and the arc discharge. Liquid oxygen isfed into the arc and partly dissociated, the excess liquid oxygencausing the arc to be quenched. The dissociated atoms either recombinewith themselves or react with oxygen molecules to form ozone. Thesolution of ozone and liquid oxygen is passed to a liquid collectionchamber while the gaseous products of the arc discharge, includingozone, are passed to a gas collection chamber. The ozone may berecovered by a conventional recovery process.

Although it is not known with theoretical exactness whether theproduction of ozone arises from the action of high energy atoms, ions orradiation, experimental results teach that ozone may be successfullyrecovered by quenching the arc discharge of a plasma generator withliquid oxygen. It is theorized that the ozone is produced by the highvelocity helium atoms, excited atoms or by Patented Mar. 14, 1967protons. The ozone yields may be controlled by varying the power levelor by varying the liquid oxygen flow.

While the specification concludes with claims which particularly pointout and distinctly claim the subject matter regarding the invention, itis believed the invention will be better understood from the followingdescription taken in connection with the accompanying drawings:

FIGURE 1 is a diagrammatic illustration of the apparatus employed in aproduction of ozone by the use of a plasma jet;

FIGURE 2 is a fragmentary View, partly in section, of the apparatusemployed particularly illustrating the plasma generator;

FIGURE 3 is a fragmentary view, partly in section, of apparatus employedparticularly showing the oxygen feed ring and liquid oxygen feed ring;

FIGURE 4 is a cross-sectional view of the oxygen feed ring taken alongline 4-4 of FIGURE 3;

FIGURE 5 is a cross-sectional view of the liquid oxygen feed ring takenalong line 5-5 of FIGURE 3;

FIGURE 6 is a cross-sectional view of the inert gas distributor ringtaken along line 66 of'FIGUR-E 2;

'FIGURES 7 and 8 are graphical illustrations of the results of sampleruns conducted for the production of ozone in accordance with theprinciples of this invention.

Referring now to FIGURE 1, there is shown a diagrammatic illustration ofthe apparatus 1t) employed in the production of ozone by the use of aplasma jet.

A coaxial jet-electrode plasma generator 11, having an inert carrier gasinput 12,'is utilized for generation of the arc discharge and plasma. Asuitable power source 13 which may have an output of, for example, 0 tovolts at O to 750 amperes, is connected across the electrodes of theplasma generator. The arc may be initiated by means of a high frequencystarter (not shown) in the power source 13, or by shorting out theelectrode with a shorting rod.

The inert gas plasma carrier, which may be helium or argon, serves tocarry the generated plasma past an oxygen feed ring 14 through whichoxygen is introduced into the area of the arc and path of the plasma.Aflixed directly below the oxygen feed ring is a liquid oxygen feed ring15 to which a suitable source of liquid oxygen is connected. The liquidoxygen both evaporates and partly dissociates due to the high thermalenergy pro duced by the helium arc. The dissociated atoms then recombineeither with themselves or react with oxygen molecules pro-duced. The arcis quenched by the ex cess liquid oxygen being fed to ring 15 and theozone is translated or carried out of the reaction zone by the excessliquid oxygen to the ozone recovery system 16.

The ozone recovery system comprises a water-cooled reaction chamber 17,a Dewar adapter ring 18 and a Dewar 19 for collecting the ozone-liquidoxygen solution. Suitable connection is made to a gas storage chamber 29for recovery of the ozone-containing gases. .The ozone in the liquidoxygen solution and in the gases may be recovered by any known process,such as, for example, absorption by silica gel.

Plasma generators, in general, are known in the art and have been foundsuitable for a variety of uses. Such plasma generators generally providean electric are which is condensed or constricted into a smallercircular crosssection than would ordinarily exist in an open arc-typedevice. This construction generates a very high temperature (l0,000 K.)so that a superheated plasma working fluid may be ejected through asuitable nozzle structure and used in any desired manner. The mass flowthrough the nozzle structure and the composition of the plasmadetermines the use to which the plasma genera- 3 tor is put. Plasmagenerators have been used elfectively for cutting, welding, metalspraying and chemical processing. In the chemical processing area,plasma generators have opened the possibility for the production of newalloys and compositions nad processing of less commonly used materials.

Referring to FIGURE 2, there is illustrated a coaxial jet-electrodeplasma generator for use in this invention. Plasma generator 11comprises a high-pressure, cylindrical housing having a water-cooledcathode assembly and a water-cooled anode assembly 26 separated by aninsulative nylon cathode enclosure member 27.

Cathode assembly 25 comprises a hollow cathode support 30 having a coverplate 32. The inner walls 33 and 34 of the cathode support 30 and coverplate 32, respectively, define a cathode cooling chamber 35 providedwith suitable inlet and outlet openings (not shown) for connecting thecooling chamber 35 to a suitable source of coolant, such as water. Theouter surface of cathode support 35 is provided, along its central axis,with a hollow cylindrical extension 36 for supporting the thoriatedtungsten cathode electrode 37 in a manner such that the tip 38 ofcathode 37 protrudes beyond the cylindrical extension 36 and coaxiallywith the anode assembly 26.

The anode assembly 26 comprises a hollow anode support 40 within whichis mounted a hollow copper anode electrode 41. The inner wall 42 ofanode 41 converges from the upper end of the anode 41 towards itsvertical axis forming, thereby, a nozzle-like arc chamber 39 which meetsat its apex with the cylindrical passage 43 formed by the inner wall 42of the lower end of anode 41. The outer wall 44 of anode 41 and theinner wall 45 of anode support 40 define the anode cooling chamber 46having an inlet 47 and outlet 48 con nected to a suitable source ofcoolant.

The cathode and anode assemblies 25 and 26, respectively, are rigidlysecured by a threaded cover member or collar 49 in threaded engagementwith anode support 40. To this end, nylon enclosure member 27 isprovided with a threaded opening 50 and flange 51 which seats on the topwall surface of anode support 40. Suitable fastening means, such asscrew 52, serves to fasten the nylon enclosure member 27 around cathodesupport and cover member 49 maintains the units tightly secured by theforce applied on flange 51 of nylon enclosure member 27. For properlysealing the mating surfaces of the various component parts, 0 rings 53are utilized in a manner well known in the art.

To effectively distribute the flow of the carrier gas in the arc chamber39, a gas distributor plate 60, more clearly shown in FIGURE 6, ismounted around the cylindrical extension 36 of the cathode support 30.The outer wall of cathode support 30 is recessed in the area directlyadjacent the extension 36 to provide a chamber 59 in which the carriergas may circulate before passing through openings 61 of the distributorplate. Conduit 62, which is connected to a suitable source of inert gas,such as helium or argon, extends through openings 63 and 64 in coverplate 32 and cathode support 3%), respectively, and is terminated flushwith the recessed walls of cathode support 30.

In the operation of the plasma generator 11, prior to striking the arc,the arc chamber 39 is pressurized by injecting through the conduit 62 aninert gas, such as helium or argon. The gas will in turn flow overdistributing plate 60, through openings 61 and into the arc chamber 39.The distributor plate 60 causes the gas to flow evenly around thecathode 37 and parallel to its axis. Anode 41 forms a nozzle with aconverging throat which concentrates the fiow of inert gas past the tip38 of the cathode 37 in th area of the arc discharge between thecoacting anode and cathode electrodes 41 and 37, respectively.

For generating the arc discharge, the cathode electrode 37 and anodeelectrode 41 of the plasma generator 11 4% are provided with suitableterminals (not shown) which are connected to a conventional low voltage,high current power source which may be either A.C. or DC. as desired. Inany manner known in the art, the output of the power source 13 is madevariable to provide a variable power level input to the plasmagenerator.

Starting the arc may be accomplished by means of a high frequencystarter in the power source 13 or by shorting the electrodes with agraphite rod (not shown). If desirable, the arc may be initiated byplacing a small piece of fuse wire between the anode 41 and cathode 37.This wire will melt when power is applied and the arc will continue.

After the arc is initiated, the arc discharge will be maintained betweenthe cathode 37 and the anode 41. The tip 3d of the cathode 37 extendsslightly into the cylindrical passage 43 formed by the inner wall 42 ofanode 41 so that the arc will be formed in the constricted chamber. Theconcentrated high pressure inert gas flow past tip 38 of the cathode 37will cause the arc to extend downwardly through the passage 43 andthrough the central openings 68, 69 of the oxygen feed ring 14 and theliquid oxygen feed ring 15, respectively. The anode nozzle structurecauses the plasma produced to exit through the oxygen and liquid oxygenfeed rings 14 and 15, respectively.

The coolant fluids in chambers 35 and 45 of cathode 37 and anode 41,respectively, serve to maintain the average temperature of the componentparts of the plasma generator 11 below the melting point of thematerials from which they are constructed. These parts may beconstructed from any suitable good heat conductive material andelectrically conductive material, where electrical continuity isdesired. For example, the cathode 37 is of thoriated tungsten While thecathode assembly 25 is made of copper. Anode 41 may likewise be made ofcopper, while the anode support 49 and collar 49 may be made ofstainless steel.

Referring now to FIGURES 3 and 5, there is shown in detail the oxygenfeed ring 14 and the liquid oxygen feed ring 15, which are mountedbetween the plasma generator 11 and the water-cooled reaction chamber 17of the ozone recovery system 16 by suitable fastening means extendingthrough the openings 72. Affixed within the oxygen feed ring 14 is astainless steel insert or channel member 73 having a central bore fordefining the opening or passage 68 extending along the vertical axis ofthe feed ring 14. Suitable inlet and outlet openings 74 and 75 areprovided along the horizontal axis of the oxygen feed ring 14. Inletcoolant conduit 76 is arranged within inlet 74, while an outlet conduit77 is arranged within inlet 75. The inlet and outlet conduits 76 and 77are connected to a suitable source of coolant medium such as, forexample, water for providing coolant within the chamber 80. The matingsurfaces of insert 73 and liquid oxygen feed ring 14 are sealed by meansof 0 rings 81 in a manner well known in the art.

Oxygen is introduced into the chamber 63 by means of conduit 82 arrangedto be received within aligned openin s 83 and $4 extending along thehorizontal axis of the oxygen feed ring 14 and insert 73, respectively.One end of opening 83 is threaded and receives a fitting 85 throughwhich the conduit 82 is connected. 0 ring 86 serves to seal the fitting85 within the opening 84 insert 73.

For purposes of rapid quenching, the liquid oxygen feed ring 15 isarranged adjacent and below the oxygen feed ring 14 and includes meansto be connected to a suitable source of liquid oxygen. To this end,there is provided along the horizontal axis of liquid oxygen feed ring15, an opening 37 within which is mounted conduit 88. Mounted within thecentral chamber of the liquid oxygen feed ring 15 is a stainless steelliquid oxygen distributor insert 39 which divides the chamber into anouter passage and an inner passage. Liquid oxygen entering throughconduit 88 enters the outer passage and circulates around the insertentering the central chamber through a plurality of openings 90 providedalong the periphery of the insert 89. The number of openings 90 may bevaried as desired dependent upon the volume of liquid oxygen flow.

The liquid oxygen entering the central chamber is partly dissociated bythe arc. The dissociated atoms then recombine either with themselves orreact with oxygen molecules to produce ozone. The are is quenched by theexcess liquid oxygen and the resultant reaction products then are passedto the ozone recovery system 16 through the water-cooled reactionchamber 17. The water-cooled reaction chamber 17 includes a centralconduit 91 having an outer jacket 92 which is provided with a suitablecoolant inlet and outlet 93 and 94, respectively, to permit cooling ofthe reaction products as they are passed to the recovery system.

It should be readily appreciated that the various fluid conduits may bearranged with suitable control valves in a manner well known in the artto control the flow of the fluid into the system so as to providevarious levels of oxygen flow, liquid oxygen flow, or coolant flow.

We have found that when subjecting oxygen to the arc the results of theexit gas stream analysis. It was found that in the second run where theliquid ozone-oxygen collection Dewar was not pre-cooled, the ozonevolume by percent was considerably increased.

TABLE 2.OZO; TE FORMATION USING LIQUID OXYGEN (LOX) QUENCH EFFLUENT GASSTREAM ANALYSIS Helium Liquid Are Characteristics Ozone, Flow, OxygenVol. liters/min Flow, Percent liters/min. Volts Amps. Kw.

1 The liquid ozone-oxygen collection Dewar was not preeooled with liquidoxygen.

The production of ozone by the inert gas plasma jet may be varied byvarying the power level, varying the liquid oxygen (LOX) flow or byvarying both the power level and the liquid oxygen flow. Table 3 showsthe effects on the production of ozone in the helium plasma jet withvarying power level.

TABLE 3 Are Characteristics Mtge- 26 28 28.5 29 29 29.5 28 27.5 28.8Amperage 340 360 350 320 310 280 320 315 300 Kilcwatts" 8.85 10.05 10.09.3 9 8.3 9.95 8.65 8.65 Helium flow, l./n1in 12.2 14.1 15.2 15.2 .15215.2 18.0 18.9 21.7 Keal/Moie He 141 138 128 119 115 106 97 88 76 LiquidOxygen flow, l./min- 3 3 3 3 3 3 3 3 Ozone Yield:

Weight percent 0.24 0.20 0.29 0.46 0.38 0.23 0.35 0.23 0.23 Lbs/hr.collected 0.78 0.49 0.77 1.13 1.17 0.57 1.07 0.62 0.61 Lbs/hr. liquidoxygen fiow 1.08 0.00 1.30 2.06 1.70 1.06 1.58 1.06 1.05

discharge of aninert gas plasma jet and rapidly quenching the arcdischarge with liquid oxygen, ozone is produced. The liquid oxygen isallowed to flow fast enough through the liquid oxygen feed ring 15 so asto provide an excess of liquid oxygen which is not dissociated forquenching the arc and carrying the ozone produced to a Dewar fiask 19 orother suitable collection means at the bottom of the reaction chamber17. The gaseous products may becollected in a separate gas storagechamber 20, and the ozone may be recovered from the solution and fromthe gas by conventional processes.

If desired, the gaseous oxygen feed ring 14 may be removed, and it hasbeen found that there is no effect on the ozone produced in solution.The following table summarizes the results of several runs using theapparatus hereinbefore described. The determination of ozone content ofthe liquid oxygen-ozone mixture was made by the evaporation method. Thevapor pressure and boiling point of a concentrated sample were identicalwith those of ozone.

The results of Table 3 are illustrated graphically in FIGURE 7 which isa plot of ozone yields in lbs/hr. vs. power level. Power level andhelium flow have been combined as one variable as follows:

kw. to arc l434 KcaL/min. kw. Helium flow l./min. X 00907 mole/1.

(2) Power 1eve1=Keal./mo1e He (1) Power level TABLE 1.OZONE FORMATIONUSING LIQUID OXYGEN (LOX) QUENCH 1 Oxygen feed ring removed. 2 Verysmall.

A series of runs were made to analyze the exit gas stream, that is, todetermine the amount of ozone in the gas from the plasma jet collectedbeyond the liquid ozoneon the total liquid oxygen (LOX) flow fed intothe plasma jet from the plasma generator. I

As hereinbefore mentoned, the amount of ozone prooxygen recovery system.The following table summarizes duced can also be varied by maintainingthe power level constant and varying the liquid oxygen (LOX) flow.Although the weight by percent of ozone produced varies appreciably withliquid oxygen (LOX) flow, the production of ozone in lbs./ hr. reaches amaximum with a liquid oxygen (LOX) how of three liters per minute(l./min.) and a. power level of between 110 to 120 KcaL/mole He. Table 4illustrates the eitect on ozone yield of varying the li uid oxygen (LOX)tlow at a power level of 111 KcaL/mole He.

TABLE 4 Are Characteristics:

Voltage Amperage 340 340 345 345 Kilowatts.

Helium flow, 1 Kcal/Molc He.

Liquid Oxygen flow, liters/min 1. 25 2 4 5 Ozone Yield:

Weight Percent 0. 23 0. 23 0.21 O. 20 Lbs/hr. collected 0. 35 0. 63 1.O4 1. O1 Lbs/hr. liquid oxygen flow O. 44 0. 7 1. 24 1. 35

TABLE 5 Power Helium Oxygen Vol. Ozone Run (kw.) Flow F w Percent Yield(L/min.) (l./min.) O (g./l1r.)

10.7 15. 2 137 0. 001 O. '28 10. 5 l5. 2 191 0.011 2. 5 1 10. 6 15. 2216 0. 020 5. 26 10.7 15. 2 218 0. 025 G. 42 10. 1 l5. 2 268 0. 045 15.10. 0 l5. 2 340 0. 057 22. 0 10. 15. 2 520 0. 059 36. 3 10. 5 15. 2 5850. 008 48. 6 10. 5 15. 2 558 0. 078 49. 7 10. 5 15. 2 185 0. 085 48. 3

Referring to FIGURE 8, it should be noted that the maximum gas flowobtainable before liquid oxygen started to flow from the water-cooledchamber was 600 liters/ min. This maximum fiow leaves a gap between thegas and liquid experiments of some 500 liters/min. (gas flow). Also, theslope of the gas-production curve deviates from the extension of theslope of the liquid oxygen flow curve (expressed in gas flow units,liters/ min.). This is theorized to be due to the loss of oxygen byevaporation in the liquid experiments. The ozone may be recovered fromthe collection chamber 19 by any suitable process, such as adsorption onsilica gel or adsorption in a suitable solvent.

Although particular embodiments of the subject invention have beendescribed, many modifications may be made, and it is intended bytheappended claims to cover all such modifications which fall within thetrue spirit and scope of the invention.

What is claimed is:

1. A method of producing ozone in a solution of liquid oxygen comprisingthe steps of: subjecting a flow of inert gas to an arc discharge,introducing liquid oxygen into said arc discharge whereby said liquidoxygen is partly dissociated, quenching the are discharge with theexcess liquid oxygen and passing the reaction products of said aredischarge to a storage chamber.

2. A method of producing ozone as set forth in claim 1 wherein saidinert gas is helium.

3. A method of producing ozone as set forth in claim 1 wherein saidinert gas is argon.

A method of producing ozone in a solution of liquid oxygen comprisingthe steps of: subjecting a flow of inert gas under pressure to an arcdischarge, subjecting a fiow of liquid oxygen to said are discharge forpartly dissociating said liquid oxygen, rapidly quenching the arcdischarge with the excess liquid oxygen, and rapidly passing theproducts of said are discharge to a storage chamber.

5. A method of producing ozone comprising the steps of: subjecting aflow of inert gas to an arc discharge, introducing gaseous oxygen in thevicinity of said are discharge, introducing liquid oxygen into said arcdischarge for partly dissociating said liquid oxygen, quenching the arcdischarge with the excess liquid oxygen and passing the products of saidarc discharge to a storage chamber.

6. A method of producing ozone as set forth in claim 5 wherein saidinert gas is helium.

7. A method of producing ozone as set forth in claim 5 wherein saidinert gas is argon.

8. A method of producing ozone comprising the steps of: subjecting aflow of inert gas to an arc discharge for producing a high energyplasma, introducing gaseous oxygen in the vicinity of said plasma andsaid are discharge, introducing liquid oxygen into said plasma and saidare discharge whereby said liquid oxygen is partly dissociated,quenching the arc discharge with the excess liquid oxygen, reacting thedissociated atoms of the liquid oxygen with themselves and oxygenmolecules, and passing the excess liquid oxygen and reaction products insolution to a first storage chamber, and passing the gaseous reactionproducts to a second storage chamher.

9. A method of producing ozone in a solution of liquid oxygen comprisingthe steps of: subjecting a flow of inert gas in a range of 10 to 25liters/min. to an arc discharge capable of producing a high energyplasma at a power level in a range of to 150 Kcal./mole gas, rapidlyquenching the arc discharge with the liquid oxygen flowing at a ratewithin the range of 1 to 6 liters/min. and rapidly passing the reactionproducts to a storage chamber.

10. The method of producing ozone as set forth in claim 9 wherein saidinert gas is helium.

11. The method of producing ozone as set forth in claim 9 wherein saidinert gas is argon.

12. The method of producing ozone as set forth in claim 9 wherein saidpower level is within the range of to KcaL/mole and said liquid oxygenflow is approximately 3 liters/min.

References Cited by the Examiner UNITED STATES PATENTS Re. 25,218 8/1962Schallus et al. 204178 906,468 12/1908 Steynis 204176 1,074,106 9/1913Dumars 204l76 2,271,895 2/1942 Hartman 204l76 2,992,540 7/1961 Grosse etal. 62-48 3,062,730 11/1962 Ruehrwein 204176 3,090,745 5/1963 Berghavs2043l2 JOHN H. MACK, Primary Examiner. R, K. MiHALEK, AssistantExaminer,

1. A METHOD OF PRODUCING OZONE IN A SOLUTION OF LIQUID OXYGEN COMPRISINGTHE STEPS OF: SUBJECTING A FLOW OF INERT GAS TO AN ARC DISCHARGE,INTRODUCING LIQUID OXYGEN INTO SAID ARC DISCHARGE WHEREBY SAID LIQUIDOXYGEN IS PARTLY DISSOCIATED, QUENCHING THE ARC DISCHARGE WITH THEEXCESS LIQUID OXYGEN AND PASSING THE REACTION PRODUCTS OF SAID ARCDISCHARGE TO A STORAGE CHAMBER.